Methods for treating an object with chlorine dioxide

ABSTRACT

The present disclosure relates to a method for treating an object with chlorine dioxide gas, comprising contacting the object with chlorine dioxide gas while exposing the object to less than 1000 lux of light. The disclosed method minimizes chlorine containing residue on the surface of the object. The object can be a raw agricultural commodity (RAC) such as a raw fruit or vegetable.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.61/919,290, filed Dec. 20, 2013, which is hereby incorporated herein byreference in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to a method for treating an object withchlorine dioxide gas while minimizing chlorine-containing residue on theobject, comprising contacting the object with chlorine dioxide gas whileexposing the object to minimal amounts of light. More particularly, thepresent disclosure relates to a method of reducing and eliminatingchlorate and perchlorate by-products formed when using chlorine dioxidegas to disinfect raw agricultural commodities.

BACKGROUND

Chlorine dioxide has been used to kill biological contaminants such asmicroorganisms, mold, fungi, yeast and bacteria in water and onsurfaces. Chlorine dioxide in solution has recently been used todisinfect raw agricultural commodities (RACs) rinse waters. The primarydisinfection by-products of water disinfection using chlorine dioxidehave been chlorate and chlorite ions. Because of concern about chlorite,chlorate and also perchlorate ions, governmental regulations requirethat RACs rinsed in water treated with chlorine dioxide must be rinsedwith potable water to remove any of these residues. Additionally,chlorine dioxide in rinse water solutions offer little removal oforganisms on the surfaces of RACs.

Therefore, there is a need for a method of treating objects such as RACswith chlorine dioxide where undesirable by-products are minimized whilesufficiently treating bacteria on the surface of RACs.

SUMMARY OF THE DISCLOSURE

The present disclosure relates to a method for treating the surface ofan object with chlorine dioxide gas while minimizing the intensity oflight to thereby reduce chlorine containing residue on the surface ofthe object.

The present disclosure relates to a method for treating an object withchlorine dioxide gas while minimizing chlorine containing residue on theobject, comprising contacting the object with chlorine dioxide gas whileexposing the object to less than 1000 lux of light. In some embodiments,the exposing step comprises exposing the object to less than 200 lux oflight. In some embodiments, the object is contacted with chlorinedioxide in a substantially dark or dark environment. In someembodiments, the object comprises a raw agricultural product. In someembodiments the raw agricultural product includes a fruit, a vegetableor a combination thereof.

In certain embodiments, the method further comprises the step ofgenerating the chlorine gas by mixing dry particles of a chlorinedioxide precursor and a proton generating species. In some embodiments,the chlorine dioxide gas is generated by mixing a sodium chloritesolution and hydrochloric acid solution. In certain embodiments, thechlorine dioxide concentration adjacent to the object is 5 mg/L or lessor 2 mg/L or less. In some embodiments, the object is contacted withchlorine dioxide for at least 5 minutes. In some embodiments, thetreating step is at a humidity of 70% or less.

In some embodiments, the total amount of chlorate and perchlorate formedon the surface of the object from said contacting step is 190 μg/kg ofthe object or less. In some embodiments, the total amount of chlorateformed on the surface of the object from said contacting step is 160μg/kg or less. In some embodiments, the total amount of perchlorateformed on the surface of the object is 30 μg/kg or less.

The details of one or more embodiments are set forth in the descriptionbelow. Other features, objects, and advantages will be apparent from thedescription, the figure and the claims.

BRIEF DESCRIPTION OF THE FIGURE

FIG. 1 depicts a graph of the chlorine gas production over time under avariety of conditions.

DETAILED DESCRIPTION

The present disclosure relates to a method for treating an object withchlorine dioxide gas, comprising contacting the object with chlorinedioxide gas while exposing the object to less than 1000 lux of light.The method thereby minimizes chlorine-containing residue such aschlorate, chlorite, and perchlorate ions on the object.

The chlorine dioxide for use in treating the object can be producedusing any method known in the art. The term “treating” as used hereinincludes, but is not limited to, “oxidizing,” “sanitizing,”“disinfecting” and “sterilizing.”

In certain embodiments, chlorine dioxide gas can be produced by mixingdry particles of a chlorine dioxide precursor and a proton generatingspecies. The chlorine dioxide precursor can be selected from anycomposition capable of producing chlorine dioxide gas when mixed with aproton-generating species. In some embodiments, the chlorine dioxideprecursor includes a metal chlorite, metal chlorate, chloric acid,hypochlorous acid, or mixtures thereof. In some embodiments, the metalchlorites and chlorates are in the form of alkali metal or alkalineearth metal chlorites and chlorates. Exemplary metal chlorites include,but are not limited to, sodium chlorite, barium chlorite, calciumchlorite, lithium chlorite, potassium chlorite, magnesium chlorite, andmixtures thereof. Exemplary metal chlorates include, but are not limitedto, sodium chlorate, lithium chlorate, potassium chlorate, magnesiumchlorate, barium chlorate, and mixtures thereof.

The chlorine dioxide precursor can be provided in any form that allowsit to react with protons to produce chlorine dioxide. In someembodiments, the chlorine dioxide precursor is in the form of a powder.In some embodiments, the chlorine dioxide precursor is impregnated in aporous carrier. In some embodiments, the porous carrier is inert. Insome embodiments, the porous carrier has pores, channels, or the likelocated therein. Exemplary porous carriers include, but are not limitedto, silica, pumice, diatomaceous earth, bentonite, clay, porous polymer,alumina, zeolite (e.g., zeolite crystals), or mixtures thereof. In someembodiments, the porous carrier is uniformly impregnated throughout thevolume of the porous carrier via the pores, channels, and the like, withthe at least one chlorine dioxide precursor.

In some embodiments, the porous carrier is impregnated with the chlorinedioxide precursor by using a porous carrier that has a low moisturecontent. In some embodiments, the low moisture content is 5% or less(e.g., 4% or less, 3% or less, 2% or less, or 1% or less) by weight. Insome embodiments, the porous carrier has an initial moisture contentabove 5% and thus can be dehydrated to produce a moisture content of 5%or less. In some embodiments, the dehydrated porous carrier is thenimmersed in or sprayed with an aqueous solution of the chlorine dioxideprecursor at an elevated temperature (e.g., in the range from 120° F. to190° F.) and the resulting slurry is thoroughly mixed. In someembodiments, the mixed slurry is then air-dried to a moisture level offrom 0% to 20% (e.g., from 2% to 18%, from 4% to 16%, from 6% to 14%,from 8% to 12%) by weight to produce the impregnate (i.e., chlorinedioxide precursor impregnated in a porous carrier) disclosed herein. Insome embodiments, the impregnate disclosed herein can be preparedwithout a drying step by calculating the amount of the aqueous solutionof the chlorine dioxide precursor needed to achieve the desired finalmoisture level (e.g., from 0% to 20%, from 2% to 18%, from 4% to 16%,from 6% to 14%, from 8% to 12% by weight) and adding this amount of theaqueous solution to the dehydrated porous carrier to impregnate theporous carrier. In some embodiments, the porous carrier include from 1%to 50% chlorine dioxide precursor (e.g., from 5% to 45%, from 1% to 35%,from 10% to 30%), from 0% to 20% water (e.g., 15% or less, 10% or less,5% or less), and from 50% to 98.5% porous carrier (e.g., from 55% to95%, from 60% to 90%, from 65% to 85%) by weight. In some embodiments,the porous carrier can include from 1% to 35% chlorine dioxideprecursor, less than 5% water, and from 65% to 94.5% porous carrier byweight. In some embodiments, the chlorine dioxide is impregnated inzeolite crystals as described above and as described in U.S. Pat. Nos.5,567,405; 5,573,743; 5,730,948; 5,776,850; 5,853,689; 5,885,543;6,174,508; 6,379,643; 6,423,289; 7,347,994; and 7,922,992, which areincorporated by reference in their entirety.

In some embodiments, the chlorine dioxide precursor is impregnated intoa porous carrier and treated with a base. In some embodiments, the baseis any suitable base that can reduce the available protons and inhibitthe reaction until the proton-generating species overcomes the base andreacts with the chlorine dioxide precursor, to enhance shelf stabilityand slow the reaction rate once the mixture is activated. Exemplarybases include, but are not limited to, potassium hydroxide, sodiumhydroxide, calcium hydroxide, or a blend thereof.

A proton-generating species as disclosed herein can be any compositioncapable of generating protons to react with the chlorine dioxideprecursor. In some embodiments, the proton-generating species is aninorganic acid, an organic acid, or a salt thereof. In some embodiments,the proton-generating species is in the form of an aqueous acid or ametal salt. Exemplary acids include, but are not limited to, aceticacid, citric acid, phosphoric acid, hydrochloric acid, propionic acid,sulfuric acid, and mixtures thereof. In some embodiments,proton-generating species comprises a metal salt. In some embodiments,the metal salt is a chloride, sulfate, phosphate, propionate, acetate,or citrate that combines with water to produce an acid, i.e., protons.In some embodiments, the metal is an alkali metal, alkaline earth metal,or a transition metal. Exemplary metal salts include, but are notlimited to, ferric chloride, ferric sulfate, CaCl₂, ZnSO₄, ZnCl₂, CoSO₄,CoCl₂, MnSO₄, MnCl₂, CuSO₄, CuCl₂, MgSO₄, sodium acetate, sodiumcitrate, sodium sulfate, sodium bisulfate, hydrogen phosphate, disodiumhydrogen phosphate, and mixtures thereof. In some embodiments, theproton-generating species is a metal salt that can also act as awater-retaining substance (e.g., CaCl₂, MgSO₄). In some embodiments, theacid is provided in the form of zeolite crystals impregnated with theacid and are produced by any suitable method.

In some embodiments, the proton-generating species is activated toproduce protons by contacting the proton-generating species with amoisture-containing (or water-containing) fluid. In some embodiments,the metal salt is ferric chloride, ferric sulfate, or a mixture thereof,and these iron salts can absorb water in addition to functioning as aproton-generating species. In some embodiments, the moisture-containingfluid is liquid water or an aqueous solution. In some embodiments, themoisture-containing fluid is a moisture-containing gas such as air orwater vapor. In some embodiments, the protons produced by theproton-generating species react with the chlorine dioxide precursor toproduce chlorine dioxide. The proton-generating species can also beactivated other than by exposure to a moisture-containing fluid. In someembodiments, the proton-generating species can be activated and canrelease protons upon exposure to the water in the powders or impregnatedporous carrier containing the chlorine dioxide precursor.

The proton-generating species can be provided in any form that allowsthe release of protons. In some embodiments, the proton-generatingspecies is in the form of a powder. In some embodiments, theproton-generating species is impregnated in a porous carrier. In someembodiments, the porous carrier is inert. In some embodiments, theporous carrier has pores, channels, or the like located therein.Exemplary porous carriers include, but are not limited to, silica,pumice, diatomaceous earth, bentonite, clay, porous polymer, alumina,zeolite (e.g., zeolite crystals), or mixtures thereof. In someembodiments, the porous carrier can have a particle size of from 0.02 mmto 1 inch (e.g., 0.125 inch, 0.25 inch, 0.50 inch, or 0.75 inch), intheir largest dimension. In some embodiments, the porous carrier canhave dimensions substantially equal to 0.25 inch by 0.167 inch, 0.125inch by 0.10 inch, 0.25 inch by 0.125 inch, 0.125 inch by 0.50 inch, or0.50 inch by 0.75 inch. In some embodiments, the porous carrier isuniformly impregnated throughout the volume of the porous carrier viathe pores, channels, and the like, with the at least oneproton-generating species.

In some embodiments, the porous carrier is impregnated with theproton-generating species by using a porous carrier that has a lowmoisture content. In some embodiments, the low moisture content is 5% orless (e.g., 4% or less, 3% or less, 2% or less, or 1% or less) byweight. In some embodiments, the porous carrier has an initial moisturecontent above 5% and thus can be dehydrated to produce a moisturecontent of 5% or less. In some embodiments, the dehydrated porouscarrier is then immersed in or sprayed with an aqueous solution of theproton-generating species at an elevated temperature (e.g., in the rangefrom 120° F. to 190° F.) and the resulting slurry is thoroughly mixed.In some embodiments, the mixed slurry is then air-dried to a moisturelevel of from 0% to 20% (e.g., from 2% to 18%, from 4% to 16%, from 6%to 14%, from 8% to 12%) by weight to produce an impregnate (i.e.,proton-generating species impregnated in a porous carrier). In someembodiments, the impregnate disclosed herein can be prepared without adrying step by calculating the amount of the aqueous solution of theproton-generating species needed to achieve the desired final moisturelevel (e.g., from 0% to 20%, from 2% to 18%, from 4% to 16%, from 6% to14%, from 8% to 12% by weight) and adding this amount of the aqueoussolution to the dehydrated porous carrier to impregnate the porouscarrier. In some embodiments, the porous carrier include from 1% to 50%proton-generating species (e.g., from 5% to 45%, from 1% to 35%, from10% to 30%), from 0% to 20% water (e.g., 15% or less, 10% or less, 5% orless), and from 50% to 98.5% porous carrier (e.g., from 55% to 95%, from60% to 90%, from 65% to 85%) by weight. In some embodiments, theproton-generating species is provided in excess of the stoichiometricamount required to produce chlorine dioxide gas when reacting with thechlorine dioxide precursor.

In some embodiments, the porous carrier impregnated with theproton-generating species is separate from the porous carrier that isimpregnated with the chlorine dioxide precursor. In some embodiments,the porous carrier impregnated with the proton-generating species isseparate from the porous carrier that is impregnated with the chlorinedioxide precursor and is separate from the porous carrier that isimpregnated with the water-retaining substance. In some embodiments, theporous carrier impregnated with the proton-generating species isseparate from the porous carrier that is impregnated with the chlorinedioxide precursor and water-retaining substance. In some embodiments,zeolite crystals are formed through the use of an aqueous solution ofthe proton-generating species in the manner described above with respectto the chlorine dioxide precursor.

The proton-generating species (whether impregnated in a porous carrieror not) and the chlorine dioxide precursor (whether impregnated in aporous carrier or not) can be mixed or otherwise combined. In someembodiments, the mixture is sprayed or coated on a surface. In someembodiments, the mixture is absorbed into a material such as a sponge,pad, mat, or the like. In some embodiments, the mixture can be placed ina reservoir, container, box, sachet, or the like.

In some embodiments, the proton-generating species is provided in thesame enclosure with an impregnate comprising the chlorine dioxideprecursor impregnated in a porous carrier. In some embodiments, theenclosing material can include any enclosing material that issubstantially impervious to liquid water. In some embodiments, themixture is placed in a humidity-activated sachet and enclosed within anenclosing material such as a membrane. Exemplary membranes include, butare not limited to, a polyethylene or paper filter. Exemplarycommercially available enclosing materials include, but are not limitedto, TYVEK® and GORTEX®. In some embodiments, the enclosing materialallows water vapor to enter the enclosure. In some embodiments, theenclosing material allows chlorine dioxide gas to be released from theenclosure and enter the atmosphere. In some embodiments, the enclosingmaterial is a sachet comprising three layers of membrane materialforming a two-compartment sachet to separate the proton-generatingspecies (whether impregnated in a porous carrier or not) from thechlorine dioxide precursor (whether impregnated in a porous carrier ornot). In some embodiments, the multiple layers of membrane material canbe selected from different membrane materials, wherein the permeabilityof the outer membrane can determine how fast humidity can enter thesachet to activate the precursor and the proton-generating species. Insome embodiments, the multiple layers of membrane material can beselected from different membrane materials, wherein the center membranecan determine how fast the protons from the proton-generating source canpass to the precursor to react and generate chlorine dioxide.

In some embodiments, the chlorine dioxide gas is generated by mixing asodium chlorite solution and hydrochloric acid solution.

The chlorine dioxide concentration produced adjacent the object issufficient to treat the surface. In certain embodiments, the chlorinedioxide concentration adjacent to the object is 5 mg/L or less (5 mg perliter of atmosphere surrounding the object). For example, the chlorinedioxide concentration can be 4.5 mg/L or less, 4 mg/L or less, 3.5 mg/Lor less, 3 mg/L or less, 2.5 mg/L or less, 2 mg/L or less, 1.5 mg/L orless, 1 mg/L or less, or 0.5 mg/L or less. In certain embodiments, thechlorine dioxide concentration adjacent to the object is at least 0.01mg/L (e.g., at least 0.05 mg/L, at least 0.1 mg/L, at least 0.2 mg/L, atleast 0.3 mg/L, at least 0.4 mg/L, or at least 0.5 mg/L, or at least 1mg/L). In some examples, the chlorine dioxide is produced adjacent tothe object in a closed container. In some examples, the chlorine dioxideconcentration is measured by photometric absorption techniques (e.g.,infrared spectroscopy, atomic absorption spectroscopy, etc) andspecifically is measured herein using a UV spectrophotometer in theultraviolet to visible region (e.g., at a wavelength of from 10⁻⁴ to10⁻⁵M).

In some embodiments, the surface of the object is contacted withchlorine dioxide for at least 5 minutes. For example, the object can becontacted with chlorine dioxide for at least 10 minutes, at least 15minutes, at least 20 minutes, at least 25 minutes, at least 30 minutes,at least 35 minutes, at least 40 minutes, at least 45 minutes, at least50 minutes, at least 55 minutes, at least 60 minutes, at least 75minutes, at least 90 minutes, at least 120 minutes, at least 150minutes, at least 4 hours, at least 6 hours, at least 12 hours, at least18 hours, at least 24 hours, or at least 48 hours.

The chlorine dioxide treatment can be conducted in an environment withany relative humidity consistent with the methods described herein. Insome embodiments, the chlorine dioxide treatment can be conducted with arelative humidity (with a humidity adjacent the object) of 90% or less,85% or less, 80% or less, 75% or less, 70% or less. 65% or less, 60% orless, 55% or less, 50% or less, 45% or less, 40% or less, 35% or less,30% or less, 25% or less, 20% or less, 15% or less, 10% or less, or 5%or less.

The chlorine dioxide treatment can be conducted with a low lightintensity or in the absence of light. In some embodiments, the surfaceof the object can be exposed to a light intensity of less than 1000 lux,less than 900 lux, less than 800 lux, less than 700 lux, less than 600lux, less than 500 lux, less than 400 lux, less than 300 lux, less than200 lux, less than 150 lux, less than 100 lux, less than 50 lux, lessthan 25 lux, less than 15 lux, less than 10 lux, less than 5 lux, lessthan 4 lux, less than 3 lux, less than 2 lux, less than 1 lux, less than0.5 lux, less than 0.1 lux, less than 0.05 lux, less than 0.01 lux, lessthan 0.005 lux, less than 0.001 lux, or less than 0.0005 lux. In someexamples, the object is treated with chlorine dioxide in a substantiallydark environment (greater than 0 to 1 lux) or a dark environment (0lux). The intensity of the light can be measured using a handheld luxmeter. Suitable lux meters are known in the art and commerciallyavailable from companies such as Sper Scientific, VWR, and Extech.

The chlorine dioxide treatment can occur at any temperature consistentwith the methods described herein. In some embodiments, the temperaturecan be the ambient environmental temperature. In some embodiments, thetemperature can be from 0 to 40° C. (e.g., 5-25° C.).

In some embodiments, the object can include any object where treatmentis desirable, e.g., to kill biological contaminants. In someembodiments, the object comprises a raw agricultural product. Examplesof raw agricultural products include vegetables, fruits, grains, nuts,and mixtures thereof. In some embodiments the raw agricultural productincludes a fruit, a vegetable, or a combination thereof.

The method limits the amount of chlorine-containing residue that formson the surface of the object as a result of the chlorine dioxidetreatment. In some embodiments, the total amount of chlorate andperchlorate ions formed on the surface of the object from saidcontacting step is 190 μg/kg of the object or less. For example, thetotal amount of chlorate and perchlorate ions formed can be 190 μg/kg orless, 180 μg/kg or less, 170 μg/kg or less, 160 μg/kg or less, 150 μg/kgor less, 140 μg/kg or less, 130 μg/kg or less, 120 μg/kg or less, 110μg/kg or less, 100 μg/kg or less, 90 μg/kg or less, 80 μg/kg or less, 70μg/kg or less, 60 μg/kg or less, 50 μg/kg or less, 40 μg/kg or less, 30μg/kg or less, 20 μg/kg or less, 10 μg/kg or less, 5 μg/kg or less, or 1μg/kg or less. In some embodiments, the surface of the object and theinterior surface of the container are rinsed with water after thecontacting step. The rinse waters are collected and analyzed via ionchromatography to assess the ion concentrations of interest.

In some embodiments, the amount of chlorate ions formed on the surfaceof the object from said contacting step is 160 μg/kg of the object orless. For example, the amount of chlorate ions can be 160 μg/kg or less,150 μg/kg or less, 140 μg/kg or less, 130 μg/kg or less, 120 μg/kg orless, 110 μg/kg or less, 100 μg/kg or less, 90 μg/kg or less, 80 μg/kgor less, 70 μg/kg or less, 60 μg/kg or less, 50 μg/kg or less, 40 μg/kgor less, 30 μg/kg or less, 20 μg/kg or less, 10 μg/kg or less, 5 μg/kgor less, or 1 μg/kg or less.

In some embodiments, the amount of perchlorate ions formed on thesurface of the object is 30 μg/kg of the object or less. For example,the total amount of perchlorate can be 30 μg/kg or less, 25 μg/kg orless, 20 μg/kg or less, 15 μg/kg or less, 10 μg/kg or less, 7.5 μg/kg orless, 5 μg/kg or less, 4 μg/kg or less, 3 μg/kg or less, 2 μg/kg orless, or 1 μg/kg or less.

By way of non-limiting illustration, examples of certain embodiments ofthe present disclosure are given below.

EXAMPLES Example 1 Gas Chamber Studies Confirmed Chlorine Dioxideby-Products are Influenced by Light Example 1a

Chlorine dioxide gas was generated within sealed 1 quart (0.95 L) glasscanning jars for a period of two hours during which half of the jarswere exposed to ambient light (fluorescent lighting in laboratory;estimated light intensity, 900 Lux), and half were shielded from lightby an aluminum foil wrap. The chlorine dioxide was generated within thejars from a two part dry mixture of particles within gas permeable TYVEKsachets. At the end of the two hour exposure period, the jars wereunsealed, the sachets removed, and unreacted ClO₂ vented to a hood.Residues on the walls of each jar were quantitatively recovered bywashing the walls sequentially with 4-50 mL aliquots of nanopure waterand combining the aliquots with additional water to bring the totalvolume to 250 mL. These washings were analyzed by ion chromatography forchlorate and perchlorate ions.

Based on reaction profiling of these particle mixtures, the weights ofthe particles provided within the TYVEK sachets were adjusted so that,upon reacting, a total of 1.6 mg of ClO₂ would have been produced ineach jar during the 2 hour period. Four replicate experiments wereconducted under both light and dark conditions.

Table 1a shows the concentration of perchlorate and chlorate ions (bothas sodium salts) in recovered wash water. Each value represents theaverage and standard deviation of 4 replicate experiments.

TABLE 1a Effect of light on production of chlorate and perchlorate with1.6 mg ClO₂ produced from dry reagent mixture. Condition Light DarkPerchlorate (μg/L) 456 ± 233 NDR Chlorate (μg/L) 988 ± 54  11 *NDR = NoDetectable Residue

Example 1b

Conditions are identical to those in Example 1a, except that ClO2 wasgenerated from a two-part liquid phase mixture consisting of a sodiumchlorite solution and a hydrochloric acid solution placed within TYVEKsachets. Based on reaction profiling, the volumes and concentrations ofthe two solutions were adjusted so that, upon reacting, a total of 1.6mg of ClO2 would have been produced in each jar during the 2 hourperiod. Table 1b shows the concentration of perchlorate and chlorate(both as sodium salts) in recovered wash water. Each value representsthe average and standard deviation of 4 replicate experiments.

TABLE 1b Effect of light on production of chlorate and perchlorate with1.6 mg ClO₂ produced from liquid reagent mixture. Condition Light DarkPerchlorate (μg/L) 438 ± 98 NDR Chlorate (μg/L) 2733 ± 267 <LOQ *LOQ =limit of quantification

Example 2 Gas Chamber Studies Confirmed the Formation of Chlorate andPerchlorate can Also be Influenced by as Concentration Example 2a

Conditions are identical to those in Example 1a, except that an amountof two part dry mixture was used that would produce a total of 7.8 mg ofClO2 during a two hour period. Table 2a shows the concentration ofperchlorate and chlorate (both as sodium salts) in recovered wash water.Each value represents the average and standard deviation of 4 replicateexperiments.

TABLE 2a Effect of light on production of chlorate and perchlorate with7.8 mg ClO₂ produced from dry reagent mixture. Condition Light DarkPerchlorate (μg/L) 4334 ± 838 NDR Chlorate (μg/L) 4857 ± 641 NDR

Example 2b

Conditions are identical to those in Example 1b, except that an amountof liquid phase reagent mixture was used that would produce a total of7.8 mg of ClO2 during a two hour period. Table 2b shows theconcentration of perchlorate and chlorate (both as sodium salts) inrecovered wash water. Each value represents the average and standarddeviation of 4 replicate experiments.

TABLE 2b Effect of light on production of chlorate and perchlorate with7.8 mg ClO₂ produced from liquid reagent mixture. Condition Light DarkPerchlorate (μg/L)  880 ± 211 NDR Chlorate (μg/L) 17497 ± 775 11 ± 2

Example 3 Gas Chamber Studies Show Chlorate and Perchlorate Ions can beMinimized and in the Case of Perchlorate Eliminated when Fumigation isPerformed in the Substantial Absence of Light when RACs are PresentExample 3a

Chlorine dioxide gas was generated within sealed 5.4 L glass chambers(10.8×22×22.8 cm (w×l×d) thin layer chromatography (TLC) tanks) eachcontaining a 100 g (ca.) tomato supported on a porous glass pedestal.During a 2 hour period, each tomato was exposed to 5.5 mg of ClO2 gasthat was generated from a gas permeable TYVEK sachet that had beencharged with a two part dry mixture of particles and placed inside thechamber. A magnetic stirrer allowed the circulation of gas within eachchamber. In half of the experiments, the chambers were exposed toambient light (per Example 1a), and in the other half, the chambers wereshielded from light by aluminum foil wrap.

Each chamber had a glass lid equipped with entry and exit portals thatwere sealed with 1.3 cm butyl septa. The lip of the chamber was treatedwith a light layer of silica vacuum grease so that upon addition of asachet, the chamber could be sealed.

At the end of the 2 hour exposure period, residual chlorine dioxide gaswas swept out of the chambers by passing air through the entry and exitportals and bubbling the exiting gas through a sodium thiosulfatesolution to convert the ClO₂ to sodium chloride.

Tomatoes were removed with tongs and washed with approximately 200 mL ofnanopure water to quantitatively recover surface residues. More waterwas added to bring the total volume to 250 mL in a volumetric flask.Each reaction chamber and remaining contents (glass pedestal andmagnetic stir bar) were rinsed with 100 mL of nanopure water intriplicate. The rinse water was placed in a 500 mL flask and water addedto the mark. Aliquots of wash waters were analyzed for chlorate andperchlorate ions by ion chromatography.

Based on previous reaction profiling of these particle mixtures, theweights of the particulates were adjusted so that upon reacting, a totalof 5.5 mg of ClO₂ would have been produced in each chamber during the 2hour period. Four replicate experiments were conducted under both lightand dark conditions.

Table 3a shows the concentration of perchlorate and chlorate ions (bothas sodium salts) in recovered wash water. Each value represents theaverage and standard deviation of 4 replicate experiments. Table 3a-1shows the concentration of perchlorate and chlorate ions (both as sodiumsalts) in recovered wash water from the surface of the tomato, expressedin terms of μg residue/kg tomato (or ppb).

TABLE 3a Effect of light on production of chlorate and perchlorate with5.5 mg ClO₂ produced from dry reagent mixture. Condition Light DarkTomato Rinse Perchlorate (μg/L) 22 ± 15 NDR (250 mL) Chlorate (μg/L) 66± 46 12 ± 3 Chamber Rinse Perchlorate (μg/L) 108 ± 91  NDR (500 mL)Chlorate (μg/L) 623 ± 299 5 *LOD = Limit of detection; LOD NaClO₄ = 1μg/L; LOD NaClO₃ = 1 μg/L

TABLE 3a-1 Effect of light on production of chlorate and perchloratewith 5.5 mg ClO₂ produced from dry reagent mixture. Condition Light DarkTomato Rinse Perchlorate (μg/kg) 55 2.5 (250 mL) Chlorate (μg/kg) 165 30*LOD NaClO₄ = 2.5 μg/kg (calculated from LOD for rinse water analysis)

Example 3b

Conditions are identical to those in Example 3a, except that ClO2 wasgenerated from a two-part liquid phase mixture consisting of a sodiumchlorite solution and a hydrochloric acid solution placed within theTYVEK sachets. Based on previous reaction profiling, the volumes andconcentrations of the two solutions were adjusted so that upon reacting,a total of 5.5 mg of ClO2 would have been produced in each chamberduring the 2 hour period. Table 3b shows the concentration ofperchlorate and chlorate ions (both as sodium salts) in recovered washwater. Each value represents the average and standard deviation of 4replicate experiments. Table 3b-1 shows the concentration of perchlorateand chlorate ions (both as sodium salts) that was washed off the tomatosurface, expressed as μg residue/kg tomato (or ppb).

TABLE 3b Effect of light on production of chlorate and perchlorate with5.5 mg ClO₂ produced from liquid reagent mixture. Condition Light DarkTomato Rinse Perchlorate (μg/L) 17 ± 7  NDR (250 mL) Chlorate (μg/L) 70± 12 20 ± 19 Chamber Rinse Perchlorate (μg/L) 113 ± 47  NDR (500 mL)Chlorate (μg/L) 600 ± 241 <LOQ * LOD NaClO₄ = 1 μg/L; LOD NaClO₃ = 1μg/L; LOQ NaClO₃ = 5 μg/L

TABLE 3b-1 Effect of light on production of chlorate and perchloratewith 5.5 mg ClO₂ produced from liquid reagent mixture. Condition LightDark Tomato Rinse Perchlorate (μg/kg) 43 2.5 (250 mL) Chlorate (μg/kg)175 50

Example 4 Radio Label Studies Show Chlorite Ion is Effectively Reactedon RAC Surfaces

Conditions are identical to those in Example 3b, except that radioactivechlorine dioxide (³⁶ClO₂) was generated in the chamber from a two-partliquid phase mixture consisting of radiolabelled sodium chlorite(Na³⁶ClO₂) solution and hydrochloric acid solution placed within theTYVEK sachets. Three separate experiments were conducted, two in whichthe chambers were exposed to ambient light, and one in which the chamberwas shielded from light by an aluminum foil wrap. The tomato weights inthese experiments ranged from 75 to 108 g. Tomato rinse water wasanalyzed for ³⁶Cl-chlorite, ³⁶Cl-chloride, ³⁶Cl-chlorate and³⁶Cl-perchlorate by first trapping fractions eluted from an ionchromatograph, and applying liquid scintillation counting of the trappedfractions. The mass concentrations were determined by dividing totalradioactivity of each species by their respective specific activity.

Table 4 shows the concentration of ³⁶Cl-chlorite, ³⁶Cl chloride, ³⁶Clchlorate and ³⁶Cl perchlorate (as sodium salts) in recovered tomatorinse water. Table 4-1 shows the concentration of ³⁶Cl-chlorite, ³⁶Clchloride, ³⁶Cl chlorate and ³⁶Cl perchlorate (as sodium salts) inrecovered tomato rinse water expressed as μg residue/kg tomato (or ppb).

TABLE 4 Residue speciation on tomato surfaces with 5.4 mg ³⁶ClO₂produced from liquid reagent mixture. Condition Light Light Dark Tomatoweight (g)  75  98 108 Tomato Rinse Chlorite (μg/L) <LOQ <LOQ <LOQ (250mL) Chloride (μg/L) 220 110 320 Chlorate (μg/L) 650 920  70 Perchlorate(μg/L) 110 280 NDR *LOQ(Chlorite) = 10 μg/L

TABLE 4-1 Residue speciation on tomato surfaces with 5.4 mg ³⁶ClO₂produced from liquid reagent mixture. Condition Light Light Dark Tomatoweight (kg) 0.075 0.098 0.108 Tomato Rinse Chlorite (μg/L) <LOQ <LOQ<LOQ (250 mL) Chloride (μg/L) 733 281 741 Chlorate (μg/L) 2167 2347 162Perchlorate (μg/L) 367 714 23

Example 5 Radio Label Studies Show Perchlorate is Formed in the as Phaseor on Container Walls Surfaces as a Result of Chlorine DioxideDecomposition and not as a Result of Chemistry on the Surfaces of RACs

Chamber rinse water was collected in the three experiments described inExample 4 and analyzed for ³⁶Cl-chlorite, ³⁶Cl chloride, ³⁶Cl chlorateand ³⁶Cl perchlorate by first trapping fractions eluted from an ionchromatograph, and applying liquid scintillation counting of the trappedfractions. The mass concentrations were determined by dividing totalradioactivity of each species by their respective specific activity.

Table 5 shows the concentration of ³⁶Cl-chlorite, ³⁶Cl chloride, ³⁶Clchlorate and ³⁶Cl perchlorate (as sodium salts) in recovered chamberrinse water.

TABLE 5 Residue speciation on chamber surfaces with 5.4 mg ³⁶ClO₂produced from liquid reagent mixture. Condition Light Light Dark Tomatoweight (g) 75  98 108 Chamber Rinse Chlorite (μg/L) 10 NM 10 (500 mL)Chloride (μg/L) 80 NM 80 Chlorate (μg/L) 3140 NM 10 Perchlorate (μg/L)590 1100 10 NM = Rinse water was not analyzed for chlorite, chloride orchlorate

Example 6 Residue Studies Show RACs are a Strong Sink for ChlorineDioxide and can be Used to Effectively Decrease as Concentrations Suchthat Perchlorate and Chlorate Residues are Minimized

Sets of ripened tomatoes (approximately 7 kg) were exposed to chlorinedioxide gas (50 mg/kg of tomato) in sealed containers for a two-hourperiod. Identical negative control vessels contained 7 kg of tomatoes,but were not charged with a chlorine dioxide generating system. Positivecontrol vessels contained the chlorine dioxide generating system, but notomatoes. All fumigations were conducted under conditions of reducedillumination (<5 lux). Chlorine dioxide concentrations were determinedduring fumigations at 10, 20, 30, 45, 60, 90 and 120 minutes by removing5 to 10 mL aliquots of container gas at the indicated sampling times andanalyzing the samples using a Rhodamine-B based spectrophotometric assayas described by Xin and Jinyu (1995).

FIG. 1 shows the generation of chlorine dioxide in empty andtomato-filled chambers and the theoretical concentrations of chlorinedioxide expected from the dry media. The release of chlorine dioxidefrom the dry media in the absence of tomatoes closely followed thetheoretical amounts of chlorine dioxide expected through 90 minutes. At120 minutes, chlorine dioxide concentrations, in the absence oftomatoes, fell well below expected concentrations, likely due to systemleaks or to chlorine dioxide reacting with the exposure chambersthemselves or with the silicone sealant used on the tanks. When tomatoeswere present in the treatment chambers, chlorine dioxide gas wasmeasurable only through 30 minutes for two replicates and through 60minutes for one replicate. These data clearly indicate that tomatoesacted as a chlorine dioxide sink, consistent with studies usingradiolabel showing the propensity for chlorine dioxide consumption bybiologic materials, especially those tissues with a porous surface suchas cantaloupe skin and the stem area of tomatoes.

The compositions and methods of the appended claims are not limited inscope by the specific compositions and methods described herein, whichare intended as illustrations of a few aspects of the claims and anycompositions and methods that are functionally equivalent are intendedto fall within the scope of the claims. Various modifications of thecompositions and methods in addition to those shown and described hereinare intended to fall within the scope of the appended claims. Further,while only certain representative composition materials and method stepsdisclosed herein are specifically described, other combinations of thecomposition materials and method steps also are intended to fall withinthe scope of the appended claims, even if not specifically recited.Thus, a combination of steps, elements, components, or constituents maybe explicitly mentioned herein; however, other combinations of steps,elements, components, and constituents are included, even though notexplicitly stated. The term “comprising” and variations thereof as usedherein is used synonymously with the term “including” and variationsthereof and are open, non-limiting terms. Although the terms“comprising” and “including” have been used herein to describe variousembodiments, the terms “consisting essentially of” and “consisting of”can be used in place of “comprising” and “including” to provide for morespecific embodiments of the invention and are also disclosed.

1. A method for treating an object with chlorine dioxide gas whileminimizing chlorine-containing residue on the object, comprisingcontacting the object with chlorine dioxide gas while exposing theobject to less than 1000 lux of light, wherein the chlorine dioxide gasis generated at less than 1000 lux of light, the total amount ofchlorate and perchlorate formed on the surface of the object is 190μg/kg of the object or less, and the object comprises a raw agriculturalproduct.
 2. The method of claim 1, wherein said exposing step comprisesexposing the object to less than 200 lux of light.
 3. The method ofclaim 1, wherein the chlorine dioxide concentration adjacent the objectduring said treating step is 5 mg/L or less.
 4. The method of claim 3,wherein the chlorine dioxide concentration adjacent the object duringsaid treating step is 2 mg/L or less.
 5. The method of claim 1, furthercomprising the step of generating the chlorine dioxide gas by mixing dryparticles of a chlorine dioxide precursor and a proton generatingspecies.
 6. The method of claim 1, wherein the chlorine dioxide gas isgenerated by mixing a sodium chlorite solution and hydrochloric acidsolution.
 7. (canceled)
 8. The method of claim 1, wherein the totalamount of chlorate formed on the surface of the object from saidcontacting step is 160 μg/kg of the object or less.
 9. The method ofclaim 1, wherein the total amount of perchlorate formed on the surfaceof the object from said contacting step is 30 μg/kg of the object orless.
 10. (canceled)
 11. The method of claim 1, wherein the rawagricultural product includes a fruit, a vegetable, or a combinationthereof.
 12. The method of claim 1, wherein the object is contacted withchlorine dioxide in a substantially dark or dark environment.
 13. Themethod of claim 1, wherein the object is contacted with chlorine dioxidefor at least 5 minutes.
 14. A method for treating an object withchlorine dioxide gas while minimizing chlorine-containing residue on theobject, comprising contacting the object with chlorine dioxide gas whileexposing the object to less than 1000 lux of light, wherein the chlorinedioxide gas is generated at less than 1000 lux of light, and wherein thetreating step comprises treating the object at a humidity of 70% orless.
 15. The method of claim 1, wherein the treating step comprisestreating the object at a temperature of 0-40° C.
 16. The method of claim1, wherein said exposing step comprises exposing the object to less than100 lux of light.
 17. The method of claim 14, wherein the total amountof chlorate and perchlorate formed on the surface of the object fromsaid contacting step is 190 μg/kg of the object or less.
 18. The methodof claim 14, wherein the object comprises a raw agricultural product.19. The method of claim 14, wherein said exposing step comprisesexposing the object to less than 100 lux of light.